Method and apparatus for alleviating erosion in multiple-completion wells



Aug. `12, 1969 H. l.. EHRLICH 3,460,626

METHOD AND APPARATUS FOR ALLEVIATING EROSION 1N MULTIPLWCOMPLETION WELLSFiled Maren s1. 19e? 2 sneets-sneet 1 HENRY L. EHRucmJR.

,4 INVENTOR ATTORNEY ug- 12. 1969 H. r-:HRLICH 3.460.626

METHOD ANI) APPARATUS FON ALLIVTIN EROSION 4IN MULTIPLECOMI.E'1ION WELLSFiled March 31. .1967 2 Sheets-Sheet 2 FIG. 2

HENRY L. EHRLICH, JR. INVENTOR ATTORNEY United States Patent O 3,460,626METHOD AND APPARATUS FOR ALLEVIATING EROSION IN MULTIPLE-COMPLETIONVVELLS Henry L. Ehrlich, Dallas, Tex., assignor to Mobil OilCorporation, a corporation of New York Filed Mar. 31, 1967, Ser. No.627,551 Int. Cl. E21b 43/12, 33/12, 41/00 U.S. Cl. 166-313 9 ClaimsABSTRACT OF THE DISCLOSURE This disclosure describes a well installationand method for use in multiple-completed wells subject to blast- Zoneerosion. A packer is disposed within a well between upper and lowerproduction intervals thereof. A conduit extends through the packer andterminates below the top of the upper production interval. This conduitprovides for fluid communication between the upper and lower intervals.The conduit is provided with a flow-restricting device which reduces thepressure of the fluid flowing upwardly through the conduit.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to the production of subterranean fluids through wells, and moreparticularly to well installations and methods for alleviating erosionof downhoe well equipment by detrital material contained in smhsubterranean fluids.

Description of the prior art In the petroleum industry, downhole wellequipment often is subjected to erosion due to the abrasive action ofdetrital material such as unconsolidated sand grains entrained inpetroleum fluids as they enter the well. This problem is most oftenencountered in multiple-completed wells which produce fluids from two ormore levels in a well. The -most common multiple-completed wells arethose in which oil and/or gas is produced from two or more verticallyspaced subterranean formations. Such formations may be separatelithologic units or they may be different zones of a common reservoirwhich are separated by relatively continuous strata of impermeable rocksuch as shale.

A conventional manner of dually producing such formations is to set andcement casing through both formations and then set a casing packerbetween the formations. A tubing string is extended through the packerwith its lower open end landed adjacent the lower productive formation.The casing packer thus effectively seals off the lannular space betweenthe tubing and casing and isolates the lower formation, which is influid communication with the interior of the tubing string, from theupper formation. The fluid from the lower formation thus flows throughthe tubing to the surface of the well or wellhead separately from theuid from the upper formation which is produced through perforations inthe casing into the annulus between the casing and the tubing string.The uid from the upper formation flows to the wellhead either directlythrough the annulus or through an additional tubing string.

Another form of multiple-completed well is somewhat similar to thatdescribed above except that the fluids from the two or more formationsinvolved are produced through the tubing string. In this arrangement,the tubing string normally extends past the upper formation and througha packer as described above. The tubing string is provided with acomminglng tool, normally positioned in the vicinity of the upperproductive formation, which 3,460,626 Patented Aug. 12, 1969 ICCcommingles the fluids from the upper and lower formations. Thecommingled uids then are withdrawn to the surface of the well throughthe tubing string.

In each of the above-described forms of multiplecompletions, a sectionof pipe, such as well tubing, eX- tends past a productive formation andthus is exposed to the produced subterranean fluid as it enters the wellthrough perforations in the wall of the casing. The uid usually is undersubstantial pressure and passes from the productive formation throughthe restricted perforations in the casing at high velocities and injetted iow courses. This particularly is true where the liuid beingproduced is comprised primarily of gas. Such uid often has a content ofsand or other particulate detrital material which impinges against thepipe surface adjacent the perforations. Such detrital material entrainedin the incoming fluid abrades and erodes the pipe surface, thus leadingto pipe failure, and .also intensifying the corrosion of the pipe.

In the past, numerous conventional techniques have been employed inattempts to protect tubing surfaces and to prevent erosion thereof.Typically, these techniques involve the provision of so-calledblast-zone protectors about the tubing adjacent the upper formation.Blast-zone protectors may be utilized in well installations providingfor commingled production, such yas disclosed in U.S. Patent No.3,283,570 to I. W. Hodges, or in well installations providing forseparate production, such as disclosed in U.S. Patent No. 3,294,122 toL. G. Sharp. Such blast-zone protectors may take numerous forms. Onemeans proposed for providing blast-zone protection involves wrapping oflayers of lead around the tubing on the theory that a malleable materialwill absorb some of the kinetic energy and the detrital material morereadily than the tubing itself. Alternatively, hard brittle materials,such as ceramics and glass, and resilient materials, such `as rubber,have been employed as protective materials for the tubing. While suchtechniques have met with some success, the resilient coatings usuallyvbeing the most effective, none of these techniques has proven entirelysatisfactory.

One diiculty experienced with the heretofore proposed procedures residesin the fact that the materials used in forming the blast-zoneprotectors, even though they are sometimes more resistant to theabrasive action of the detrital materials than the metal pipe surfaces,still experience some erosion and ultimately fail; thus leaving the pipesurfaces exposed to the abrasive action of detrital materials as theyenter the well. If this condition is undetected the exposed surfaces mayfail under the erosive laction of such materials, sometimes within amatter of hours. This, of course, necessitates expensive workovers suchas withdrawing the tubing, repairing it if necessary, and providingadditional protective material. Another serious consequence of suchfailure is the placing of the respective formations directly incommunication with one another through the well. In this case,production may be obtained only from the formation of relatively highpressure and fluid from the relatively high pressure formation may flowinto the lower pressure formation. This latter situation may result insevere damage to the lower pressure formation and, in addition, thefluid may be lost through this formation to other wells.

SUMMARY OF THE INVENTION In accordance with the present invention, thereis provided a multiple-completion well installation and method in whichdownhole well equipment, such as a tubing string, need not be locatedwithin a blast-zone area where it is subject to erosion. The method ofthe invention is practiced in a well penetrating at least two verticallyspaced subterranean formations in which the pressure of the lowerformation is greater than the pressure of the upper formation. The wellis open to the lower formation through a first production interval andto the upper formation through a second production interval whichcomprises a section of perforated casing. In carrying out the method ofthe invention, fluids from the lower and upper formations are producedinto the well through the rst and second production intervals,respectively. As the fluid from the lower formation enters the well itis passed through a flow path within the well which extends from thefirst production interval to the second production interval. As thelower formation fluid is passed to the second production interval, thepressure of the lower formation fluid is reduced to a value less thanthe upper formation pressure. The lower formation fluid is commingledwithin the second production interval with the fluid from the upperformation by contacting this latter fluid as it flows into the wellthrough the casing perforaions with the lower formation fluid. Thecommingled fluids then are withdrawn from the well.

In accordance with a preferred embodiment of the invention, there isprovided a well installation which may be utilized in practicing theabove-described method. This installation includes packing meansdisposed within the well to separate the upper and lower productionintervals of the well. The packing means may be one or more conventionalcasing packers. A conduit extends upwardly through the packing means andterminates at a level below the top of the second or upper productioninterval. This conduit provides a passageway for the flow of fluid fromthe lower formation to the upper production interval. As the lowerformation fluid flows into the second production interval, it iscommingled with the fluid recovered from the upper formation. Theconduit is provided with flow-restricting means which reduces thepressure of the lower formation fluid as it passes upwardly through theconduit.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE l is an illustration, partly insection, showing one embodiment of the present invention; and

FIGURE 2 is an illustration, partly in section, showing a modifiedembodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to FIGURE l,there is shown a wellbore which extends from the surface 11 of the earthand penetrates vertically spaced subterranean formations 12 and 14. Thewell is provided with a casing 16 which is cemented as indicated byreference numeral 17. The casing and the surrounding cement sheath areprovided opposite the formation 12 with a plurality of perforations 18which define an upper production interval of the well, as indicated bybracket 19. In most instances, the production interval 19 will be formedby a plurality of circular perforations produced by a jet or gunperforating technique. It will be understood, however, that othersuitable arrangements may be used. For example, the production interval19 may be formed by so-called shop perforated or slotted pipe in whichopenings are formed prior to insertion of the casing into the well.Numerous other procedures for providing an opening in a well to the flowof subterranean fluids are well known to those skilled in the art and,accordingly, will not be described further.

A packer 21 is disposed in the well above the top of the upperproduction interval 19. The well also is provided with a tubing string22 which extends from the wellhead 24 or surface of the well through thepacker 21 to a level above the top of the upper production interval 19.Fluids from the upper formation 12 and, as explained hereinafter, fromthe lower formation 14 are produced through the interior of the tubingstring 22 and carried to the surface of the well where they are passedinto a suitable gathering line 25.

The casing 16 and surrounding cement 17 are provided opposite the lowerformation 14 with a group of perforations 27 which define a lowerproduction interval as indicated by bracket 28. The lower productioninterval may be formed by other means as will be apparent to thoseskilled in the art.

The production equipment thus far described is exemplary only and it isto be understood that other suitable arrangements consistent with thepractice of the present invention may be used. For example, the packer21 and tubing string 22 may be dispensed with and fluids may be producedto the surface of the well directly through the casing 16.Alternatively, tubing string 22 may not extend to the wellhead butinstead may terminate within or above packer 21, in which case fluidwill likewise be recovered or produced from the well through the casing16. It usually will be preferred to exten-d tubing 22 to the surface asshown for reasons of well control and manipulation and also to avoidcorrosion in the upper portions of the casing string.

It further is to be understood that, while only a single casing string16 is shown, the well may be provided with a plurality of casingstrings. For example, the well may be provided with a conductor pipe orsurface string and one or more intermediate strings, as will be readilyapparent to those skilled in the art. In addition, while the casingstring 16 is shown as extending completely to the surface of the well itwill be understood that other suitable arrangements may be used. Forexample, the perforated casing adjacent the formation 12 and/ or theformation 14 may take the form of a so-called scab liner. Such a lineror liners may occupy only selected portions of the well, such asopposite formations 12 and 14, in which case remaining portions of thewell may be uncased. Further, in certain circumstances such as where theformation 14 is not subject to sand problems, the lower completioninterval may be an open hole. In this case, the casing string 16 may beset into the top of the formation 14 and cemented in the well, and thewell then drilled deeper to provide an open hole completion. These andother completion procedures are well known to those skilled in the artand, accordingly, will not be discussed further.

As is known by those skilled in the art, the pressures of subterraneanformations normally increase with their depths. For example, an oiland/or gas reservoir found at a depth of 5,000 feet typically mayexhibit a pressure on the order of 2,000 p.s.i., whereas, a deeperunderlying reservoir found at 10,000 feet may be expected to be at apressure on the order of 4,000 p.s.i. In the method of the presentinvention, this normal order of pressure relationships is utilized toadvantage in a method of recovering fluids through a multiple-completionwell. Therefore, for the purpose of describing this method it will beassumed that the pressure of formation 14 shown in FIG- URE 1 is greaterthan the pressure of formation 12.

It will be recognized by those skilled in the art, that by reference tothe pressure of a designated formation or by the term formationpressure, is meant the pressure of the formation adjacent the well understatic conditions. This pressure may be determined for a given formationby conventional techniques. For example, the pressure of a formation inthe vicinity of a well may be determined by a so-called pressurebuild-up test in which the well is shut in for such time as is necessaryto establish a pressure equilibrium or near pressure equilibrium betweenthe well and the formation. The static downhole pressure of the wellwhen it is shut in with respect to the formation, i.e., when there is nofluid flow from the formation into the well, is, of course,substantially equivalent to the formation pressure.

It further will be recognized that the flow of fluids into the welldepends upon an established differential between the pressure within theformation penetrated by the well and the downhole pressure within thewell opposite the formation. The downhole pressure of the well at anygiven rate of production is designated as the operating pressure of thewell for this production rate and formation. The operating pressure ofthe well for a designated formation may, of course, vary widelydepending upon the conditions under which the well is operated.

Returning now to FIGURE 1, the well is provided with packing means whichseparates the upper and lower production intervals 19 and 28,respectively. As shown in FIGURE 1, this packing means may take the formof a pair of conventional casing packers 30 and 31. Extending throughthe packers 30 and 31 is a conduit 32 which provides a passageway forthe tlow of fluid recovered from the lower formation 14 upwardly to theupper production interval 19 of the well. The conduit 32 include, inaddition to certain instrumentalities described hereinafter, aperforated section 33 which provides for the entry of the lowerformation fluid into the conduit.

It will be recognized that considerable distance may separate formations12 and 14 and it usually will be desirable to utilize a plurality ofpackers as shown. This will aid in centering the conduit 32 within thewell and also will prevent the casing between these packers from beingcontacted by well fluids, thus lessening corrosion problems within thisarea. However, the packing means may take another suitable form such asa single casing packer. Also, while the conduit 32 usually will comprisea tubing string, those skilled in the art will recognize that theconduit may comprise any suitable structure. For example, in appropriatecircumstances the conduit may consist simply of the bore of aconventional packer.

As noted previously, the pressure of formation 14 is greater than thepressure of formation 12. By way of example, formation 12 may be a gasreservoir at a depth of 5,000 feet exhibiting a formation pressure ofabout 2,000 p.s.. and formation 14 may be a gas reservoir at a depth ofabout 10,000 feet and having a formation pressure of about 4,000 p.s..In view of these pressure relationships the conduit 32 is provided withflow-restricting means in order to reduce the pressure of the lowerformation fluid as `it passes from the lower production interval 28 ofthe well upwardly through the conduit 32 to the upper productioninterval 19. Desirably, the pressure of the lower formation fluid isreduced to a value such that it is approximately equal to the desiredoperating downhole pressure within the upper production interval 19.Thus, if it is desired to produce the formation 12 under a flowingpressure gradient from the formation to the well of 1,000 p.s.., suchthat the operating downhole pressure within the interval 19 is 1,000p.s.., the flow of the lower formation lluid through the conduit 32 isrestricted such that it exits from the conduit against a back pressureof about 1,000 p.s.. It is recognized that under practical operatingconditions it may be diiiicult to achieve such a pressure reductionwithin closely defined limits of accuracy. However, the pressure of thelower formation fluid should at least be reduced to a value such that itenters the upper production interval against a back pressure less thanthe pressure of the formation 12, .e., 2,000 p.s.., in the cxample givenabove. If the pressure is not reduced to at least this level thereexists the possibility of the uid from the lower formation flowing intothe upper formation 12 with the attendant deleterious results notedabove.

While the flowing pressure gradient from the formation 12 into the wellmay vary widely depending upon local conditions, it usually will bedesirable to produce the formation 12 under a pressure gradient of atleast 2000 p.s.. or of the formation pressure, whichever is greater.Therefore, it is preferred in carrying out the invention to reduce thepressure of the lower formation fluid to a value which is less than thepressure of formation 12 by at least the greater of 200 p.s.. and 10% ofthe pressure of formation 12.

IPressure reduction within the conduit 32 may be accomplished by meansof any suitable flow-restricting de- 6 vice. Thus, as shown in FIGURE 1,the conduit 32 is provided with a conventional downhole choke 34. Thesize of the choke 34 may be selected in accordance with practices Wellknown to those skilled in the art in order to achieve the desiredpressure gradient thereacross. The pressure reduction to be achievedacross the choke 34 will, of course, depend upon the frictional lossesoccurring in ow from theY lower production interval upwardly through theconduit 32 to the choke 34. Thus, if a total pressure reduction of 2,500p.s.. is desired between the upper and lower production intervals andthe frictional losses in fluid flow upwardly through the conduit 32result in a pressure gradient of p.s.., the choke should be chosen so asto achieve a pressure gradient thereacross of 2,400 p.s.. The conduit 32is also provided with a check valve 35 in order to provide forunidirectional flow from the rst production interval to the secondproduction interval. Thus, should the natural order of pressurerelationships be reversed, the valve 35 will ensure that fluid will notow from the upper production interval 19 to the lower productioninterval 28. In some instances the valve 35 will be unnecessary. Thechoke and check valve are mounted in a removable tool 36 which isthreaded to the conduit 32 as indicated by reference numeral 37. Itusually will be desirable to connect the tool 36 near or at the upperend of conduit 32 as shown in order to provide for simplicity ofinstallation and withdrawal of this tool.

The elimination of tubing, a commingling tool or other like downholewell equipment from the blast-zone area opposite the perforations 18greatly reduces the possibility of erosion of such equipment and makesunnecessary the provision of a vblast-zone protector for such equipment.In addition, by the present invention, such erosion as takes placewithin the upper production interval will usually prove to bebeneficial. ln this: regard, detrital material entrained in the fluidentering the well through perforations 18 may tend to cause additionalperforations in the casing. For example, fluid flowing through thelowermost perforation 18 may be of a velocity such that entraineddetrital material will tend to erode the opposite wall of the casing atthe area generally designated Iby reference numeral 18a, ultimatelycausing a perforation at this location. The presence of such additionalperforations will increase the cross-sectional area open to the flow offluid from the formation with the attendant result that the entraineddetrital material from the formation 12 will enter the Well at a reducedvelocity. This diminishes the ibrasive action of the entrained detritalmaterial and may allow the subsequent location of downhole equipmentwithin the blast-zone area, if this should become desirable. Forexample, after the formation of one or more additional perforations asdescribed above, the abrasive action may be reduced such that a tubingstring may be extended through interval 19 in the event it becomesdesirable to produce formations 12 and 14 separately.

If the formation 12 is a gas reservoir, and if the perforations 18 areequally open to fluid flow, gas normally will enter through each ofthese at substantially the same velocity. However, in some cases, thefluid ilowing through the lower perforations of the production interval19 may -be at a relatively low velocity as compared with fluid issuingthrough the perforations in the upper portion of the production interval19. This condition may exist, for example, where formation I12 is an oiland gas reservoir with gas production primarily through the upperperforations and oil production primarily through the lowerperforations. As will be understood by those skilled in the art, the oilnormally will enter through at a relatively low velocity with aresultant low erosion potential. Also, even though formation 12 isprimarily a gas reservoir, the flow velocity through the lowerperforations may be relatively low because of localized permeabilitydissimilarities in the formation adjacent the well. For example, thepermeability of the formation 12 7 adjacent the lower perforations maybe low due to a tight rock structure or to localized damage to theformation as may occur during completion of the well.

In View of the above discussion, it will be recognized that the locationof the upper end of conduit 32 may vary depending upon the localconditions. Usually it will be preferred to terminate the conduit 32 ata point below the bottom of the production interval 19 as shown.However, in some instances it will be possible to extend the conduit 32partially into the upper production interval 19 without serious erosionproblems. In any case, the conduit32 should terminate below the top ofthe upper production interval 19.

It usually will be desired to monitor either continuously orintermittently the production rate from the formation 14 and also thebottornhole pressure at the lower production interval 28. While, asdescribed hereinafter, such measurements can be taken through the use ofsuitable wireline tools, it sometimes may be desirable to make thesemeasurements at frequent intervals and/or over extended periods of time.In such situations, it is preferred to maintain the necessary measuringtools in the well during normal operations. A preferred installation foraccomplishing this objective is shown in FIG- URE l.

With further reference to FIGURE 1, the tubing 32 is provided with aflow measuring device 38 and a pressure measuring device 42. Themeasuring devices 38 and 42 may be of conventional design and may beprovided with suitable communication channels for telemetering thedesired information to the surface. Alternatively, the devices 38 and 42may include recording means which may be withdrawn from the well asdesired. The pressure measuring device should be located below theflow-restricting means 34 as shown in order that it may be responsive tothe downhole pressure at the lower production interval. It usually will.be desirable to similarly locate the flow meter 38 although this latterdevice may under appropriate circumstances be located at any positionwithin the flow path from the lower production interval to the upperproduction interval.

The total flow from the well may be measured at the wellhead byconventional practice. Thus, it can be seen that knowing the productionrate of the lower formation 14, the production rate from the upperformation 12 can be determined.

As noted previously, the bottornhole pressure at the upper productioninterval 19 should, during normal operation of the well, be maintainedat some desired value less than the pressure of the formation 12. Anincrease in the `bottornhole pressure will result in a lower productionrate from the formation 12, and, of course, a bottomhole pressure inexcess of the formation pressure will result in iluid ilow from the wellinto the formation with possible deleterious effects. Such a pressureincrease at interval 19 may be due to factors such as shutting in orthrottling of the well at the wellhead or a rise in the production ratefrom the lower formation 14.

With reference to FIGURE 2, there is shown a modied form of theinvention in which the flow-restricting device is adjustable andresponsive to pressure changes in the upper production interval 19.Also, in the embodiment of FIGURE 2, the packing means separating theupper and lower production intervals and the conduit providing a ow pathare fonmed as a single unit. The installation shown in FIGURE 2 isotherwise somewhat similar to that illustrated in FIGURE l and likeelements in FIGURE 2 are designated by the same reference numerals asused in FIGURE 1.

In the embodiment of FIGURE 2, the well is cased adjacent the lowerformation 14 by means of a liner 40. The liner 40 is cemented in placeand the liner and the surrounding cement sheath 42 are provided with aplurality of perforations 44. The perforations 44 dene a lowerproduction interval 46 in the well, similar to 8 the production interval28 described above with reference to FIGURE 1. The packing meansseparating the upper and lower formations takes the form of an annularplate 48 which is formed integrally with the liner 42. Extending throughthe packing element 48 is a conduit 50 similar in function to theconduit 32 in FIGURE l. This liner, packing element, and conduitinstallation may be utilized in those instances where it is not desiredto case the entire interval of the well between the upper and lowerformations. This embodiment oers certain advantages in that the completedownhole installation including the liner, packing element and conduitmay be run into place within the well as a single unit and in a singleoperation.

The conduit 50 is provided with a dow-restricting means which isresponsive to pressure changes in the upper production interval 19. Morespecifically, there is provided an adjustable flow-restricting device 54and means responsive to an increase in pressure within the upperproduction interval 19 for decreasing the rate of flow of the lowerformation iluid through the conduit 50. The flow-restricting device 54is connected in the tubing 50 by means of a threaded coupling 55. Thus,the device 54 may be withdrawn or run into place by suitable wirelinetechniques. The device S4 comprises a valve member 56 which has an upperface 57 and which is slidably mounted within an outer case 58. The valvemember is biased away from a valve seat 59 by means of a compressionspring 60 which is interposed between appropriate shoulders on the valvemember and the case as shown. Upward movement of the valve member islimited by means of a stop element 61 on the outer case.

When the valve 56 is open as shown, fluid from the lower formationtravels upwardly through the conduit 50, through passages 62, and thencethrough the throat 64 of the valve member. The compression in the spring60 and the surface area of face 57 are balanced such that the valveremains in an open position under the desired back pressure within theupper production interval 19. From an examination of FIGURE 2, it can beseen that an increase in pressure within interval 19 above the desiredlevel will cause the valve member 56 to move downwardly, thus throttlingfurther the fluid ow through the restricting means until it reaches avalue consistent with the pressure desired in interval 19. Of course,should this pressure then decrease, the valve member will open somewhatthus increasing the flow rate of the lower formation fluid as necessary.

It will be noted that the modification of FIGURE 2 does not includedownhole devices for measuring flow rate or pressure. Such productionmeasurements may be accomplished in this embodiment through theapplication of suitable wireline techniques. For example, a downholetlow meter such as that described in Godbey, I. K., New Flowmeter GivesWater-Injection Profiles, The Oil and Gas Journal, Mar. l2, 1962, pp.92-95, may be lowered to a position below interval 19 and the ilow ratefrom formation 14 measured. The flow rate of upper formation 12 then maybe determined from total production rate measurements taken at thesurface of the well. Alternatively, the production rates from formations12 and 14 may be determined by measuring the flow from the well withboth formations producing and also with formation 14 shut in. It will berecognized that downhole pressure measurements also may be taken throughthe use of suitable wireline tools.

As is known to those skilled in the art, the erosion of a surface byabrasive particles depends upon factors such as the velocity andquantity of the particles, and also their size, shape and hardness. Ofthese, the Velocity of the particles as they strike the surface usuallyis the single most important factor. While erosion and ultimate failureof well tubing may occur at low velocities depending upon localconditions, experience has shown that in most wells, blast-zone erosionbecomes significant at particle velocities of about 20 feet per second.While blast-zone protectors such as those noted above afford a measureof protection, these oftentimes are readily susceptible to erosion atthe higher particle velocities, particularly those on the order of 200feet per second and above. Accordingly, while the invention may beutilized under any conditions in which the iluid from an upper formationhas entrained therein sand or other detrital material, it isparticularly useful where particle velocities are at least 20 feet persecond, and especially so where particle velocities are at least 200feet per second.

Having described certain specific embodiments of the instant invention,it will be understood that further modifications thereof may besuggested to those skilled in the art, and it is intended to cover allsuch modifications as fall within the scope of the appended claims.

What is claimed is:

1. In the recovery of fluids through a well penetrating at least twovertically `spaced upper and lower subterranean formations, the pressureof said lower formation being greater than the pressure of said upperformation, said well being open to said lower formation through a lowerproduction interval and to said upper formation through an upperproduction interval comprising a section of perforated casing, themethod comprising:

producing fluid from said lower formation into said well through saidlower production interval, producing iluid from said upper formationinto said well through said upper production interval whereby said fluidflows into the interior of said section of casing through perforationstherein, said fluid having entrained therein abrasive detrital material,flowing said lower formation fluid through a flow path within said wellfrom said lower production interval to said upper production interval,

within said ilow path, reducing the pressure of said lower formationiluid to a value less than the pressure of said upper formation,

commingling said lower formation lluid with said upper formation iluiclby contacting said upper formation fluid as it flows into the interiorof said section of casing through the perforations therein with saidlower formation fluid, and

withdrawing said commingled iluids from said well.

2. The method of claim 1 wherein the pressure of said lower formationfluid is reduced within said flow path to a value which is lower thanthe pressure of said upper formation by at least the greater of 200p.s.i. and of the pressure of said upper formation.

3. The method of claim 1 wherein detrital material entrained in thelluid from said upper formation enters into the interior of said casingat a velocity of at least feet per second.

4. The method of claim 1 wherein detrital material entrained in theiluid from said upper formation enters into the interior of said casingat a velocity of at least .200 feet per second.

5. The method of claim 1 wherein detrital material entrained in theiluid from said upper formation erodes at least one additionalperforation in said section of casing and further comprising the stepof, subsequent to the eroding of said additional perforation, locatingdownhole equipment within said upper production interval.

6. In a well penetrating at least two vertically spaced upper and lowerformations, said well being open to said lower formation through a lowerproduction interval and to said upper formation through an upperproduction interval comprising a section of perforated casing, thecombination comprising:

packing means within said Well separating said upper and lowerproduction intervals,

a conduit extending through said packing means and terminating at alevel below the top of said upper production interval and opening intothe interior of said casing, said conduit providing a passageway for theflow of fluid recovered from said lower formation to said upperproduction interval within which said lower formation fluid iscommingled with fluid recovered from said upper formation,

adjustable ilow restricting means within said conduit for reducing thepressure of the lower formation fluid as it passes through said conduit,and

means responsive to an increase :in pressure within said well above saidpacking means for adjusting said restricting means for decreased iluidflow through said conduit.

7. In a well penetrating at least two vertically spaced upper and lowerformations, said well being open to said lower formation through a lowerproduction interval and to said upper formation through an upperproduction interval comprising a section of perforated casing, thecombination comprising:

packing means within said well separating said upper and lowerproduction intervals,

a conduit extending through said packing means and terminating at alevel below the top of said upper production interval and opening intothe interior of said casing, said conduit providing a passageway for theilow of fluid recovered from said lower formation to said upperproduction interval within which said lower formation lluid iscommingled with lluid recovered from said upper formation,

flow restricting means within said conduit for reducing the pressure ofthe lower formation fluid as it passes through said conduit, and

a check valve in said conduit allowing unidirectional ilow from saidlower production interval to said upper production interval.

8. In a well penetrating at least. two vertically spaced upper and lowerformations, said well being open to said lower formation through a lowerproduction interval and to said upper formation through an upperproduction interval comprising a section of perforated casing, thecombination comprising:

packing means within said well separating said upper and lowerproduction intervals a conduit extending through said packing means andterminating at a level below the top of said upper production intervaland opening into the interior of said casing, said conduit providing apassageway for the ilow of fluid recovered from said lower formation tosaid upper production interval within which said lower formation fluidis commingled with fluid recovered from said upper formation,

flow restricting means within said conduit for reducing the pressure ofthe lower formation iluid as it passes through said conduit, and

pressure measuring means within said passageway and located below saidilow restricting means.

9. The combination of claim 8 further comprising flow measuring meanswithin said passageway.

References Cited UNITED STATES PATENTS Re. 26,319 12/1967 Tamplen166-115 2,371,840 3/1945 Otis 166-45 X 2,531,258 1l/1950 Cranll 166-1162,649,914 8/1953. Otis 166-114 2,839,144 6/1958 Ault 166-224 X 2,869,645l/l959 Chamberlain et al. 166-115 X 3,171,483 3/1965 Fredd 166-114 X3,283,570 11/1966 Hodges 166--45 X 3,357,492 12/1967 Hubby 166-45 X3,371,717 3/1968 Chenoweth 166--148 X CHARLES E. OCONNELL, PrimaryExaminer IAN A. CALVERT, Assistant Examiner U.S. Cl. X.R. 166-115, 133,224

ggo UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3:"6O626 Dated u August l2, 1969 Inventor(s) Henry I.. Ehrlich It :lscertified that error appears in the aboveidentifed patent and that saidLetters Patent are hereby corrected as shown below:

|- Column l, line lbf, "multple-i-completed" should read"`multplycompleted; line 39, "multiple-Completed" Should read--multiply-completed--g line Lil, "multiple-completed" Should readmultiplycompletedg line 65, "multiple-completed" should readmultply-completed Column i?, line 3M, "and should read Of Column F3,line l5, "include" should read --ncludes--g line g, "QOOO" should read-200 COlUmU 6, 1H@ "brasive" should read -abrasive.

Column lO, line 72, "JAN" Should read -IAN SIGNED N'D SEALED A APR 74970 (SF-m Amm:

i WmIAll E. 'SCHUH-IER, JR.. EA'cl MOHM It cmissionefr `of Iabents

